Air Force Heating Blog

High-Efficiency Furnace Models Simplified.

We provide simple explanations of the “common high-efficiency furnace models” purchased in Calgary and area.

Furnaces have two sections. The upper cabinet houses the heat exchangers, drainage system, inducer motor and gas valve. The lower, the circuit board and blower motor.

When dealing with efficiencies and furnace models, the two key components are the gas value (gas consumption) and the blower motor (electricity).

Single Stage Furnace

These furnaces use 20-40% less gas annually. They are best suited for bungalows, open floor plans, and townhomes. They only have on or off functionality though.

  • 92-96% A.F.U.E
  • Single Stage Gas Valve
  • Single Stage Inducer motor
  • Multi-Speed PSC Blower
  • Alternating current power
  • 500 watts


Two Stage Furnace with ECM blower

Annually uses 30% less gas and 33% less electricity than a single stage high-efficiency furnace. Perfect for two-story homes and families that want more out of their heaters.

They can heat multiple levels consistently and evenly. They have two stages of output intensity like settings on a hotel desk lamp.

  • 95-96% A.F.U.E
  • 2-Stage Gas Valve (1st stage 60% of max output)
  • Single or 2 Stage Inducer motor
  • ECM Blower
  • Direct current power
  • 300 watts


Two Stage Furnace with Variable blower

These models use 30% less gas and 66% less electricity than the single stage furnace. It has an upgraded control board and an additional component added unto the ECM blower.

The unit can run continuously at very low speeds! Perfect for larger two-story homes with problematic hot or cold areas.

Also, an excellent solution when air quality concerns need addressing or you are a light sleeper. Same as ECM option but cost even less to operate.

  • 95-96% A.F.U.E
  • 2-Stage Gas Valve (1st stage 60% of max output)
  • Single or 2 Stage Inducer motor
  • Variable ECM Blower
  • 3-Phase power
  • 75 watts


Modulating Furnace with Variable Blower

These units use 8-12% less gas than a two-stage furnace. Designed primarily for large custom homes with zoning. These models offer ultimate comfort in all styles of homes and floor plans.

To get the maximum benefits from these furnaces though, they sometimes need to be paired with a costly “communicating” thermostat. They operate like a light dimmer switch. Various outputs of intensity with ease.

  • 97-98% A.F.U.E
  • Modulating gas valve (as low as 30% of max output)
  • 2 Stage Inducer motor
  • Variable ECM Blower
  • 3-Phase power
  • 75 watts

2 Stage Is Best For Calgary

This model is great for our region.

Furnaces are sized to handle the worst-case scenario or the coldest days of the year.-30 to -40 degrees Celsius days only account for 10% of the yearly runtime.

90% of the annual runtime, your furnace will just be firing on “low fire,” saving on utilities and prolonging the life of your equipment (not working as hard).

Typically, a two-stage furnace is $1000 more than its single counterpart.  The higher cost takes 3-5 years to recoup in utility savings. (depends on the size of the unit and your desired temperature).

How Does A Two-Stage Furnace WORK?

Simply put, a two-stage furnace has three positions or settings for the gas valve, the valve regulates the amount of gas burned by the unit.

When off it’s “closed.”
When the thermostat turns on, the valve goes to “partially open.” (normally 60-65% compacity)
And if the home doesn’t reach your desired temperature in a specific time, the gas valve opens to “fully open” position and gives the max heating capacity.

Not to overcomplicate things but the first stage is called “low fire” & second stage “high fire.” Two-stage furnaces also can jump straight to high fire if you raise the thermostat 3 degrees or more (if your installer sets it up correctly).

When two-stage furnaces are sized, installed and commissioned correctly, they run less often but run longer. That is the #1 reason why they can heat larger bungalows and two-story homes more consistently and evenly.